Mobility of arsenic and its compounds in soil and soil solution: The effect of soil pretreatment and extraction methods

The effect of soil extraction procedures and/or sample pretreatment (drying, freezing of the soil sample) on the extractability of arsenic and its compounds was tested. In the first part, five extraction procedures were compared with following order of extractable arsenic portions: 2 M HNO3 ≫ 0.43 M CH3COOH ≥ 0.05 M EDTA ≥ Mehlich III (0.2 M CH3COOH + 0.25 M NH4NO3 + 0.013 M HNO3 + 0.015 M NH4F + 0.001 M EDTA) extraction ≫ water). Additionally, two methods of soil solution sampling were compared, centrifugation of saturated soil and the use of suction cups. The results showed that different sample pretreatments including soil solution sampling could lead to different absolute values of mobile arsenic content in soils. However, the interpretation of the data can lead to similar conclusions as apparent from the comparison of the soil solution sampling methods (r = 0.79). For determination of arsenic compounds mild extraction procedures (0.05 M (NH4)2SO4, 0.01 M CaCl2, and water) and soil solution sampling using suction cups were compared. Regarding the real soil conditions the extraction of fresh samples and/or in situ collection of soil solution are preferred among the sample pretreatments and/or soil extraction procedures. However, chemical stabilization of the solutions should be allowed and included in the analytical procedures for determination of individual arsenic compounds.